2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
35 enum Tracing { NO_TRACE, TRACE };
37 enum Term { // The first 8 entries are reserved for PieceType
38 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
41 Score scores[TERM_NB][COLOR_NB];
43 double to_cp(Value v) { return double(v) / PawnValueEg; }
45 void add(int idx, Color c, Score s) {
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 scores[idx][WHITE] = w;
51 scores[idx][BLACK] = b;
54 std::ostream& operator<<(std::ostream& os, Score s) {
55 os << std::setw(5) << to_cp(mg_value(s)) << " "
56 << std::setw(5) << to_cp(eg_value(s));
60 std::ostream& operator<<(std::ostream& os, Term t) {
62 if (t == MATERIAL || t == IMBALANCE || t == INITIATIVE || t == TOTAL)
63 os << " ---- ----" << " | " << " ---- ----";
65 os << scores[t][WHITE] << " | " << scores[t][BLACK];
67 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
72 using namespace Trace;
76 constexpr Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
77 constexpr Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
78 constexpr Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
79 constexpr Bitboard Center = (FileDBB | FileEBB) & (Rank4BB | Rank5BB);
81 constexpr Bitboard KingFlank[FILE_NB] = {
82 QueenSide, QueenSide, QueenSide,
83 CenterFiles, CenterFiles,
84 KingSide, KingSide, KingSide
87 // Threshold for lazy and space evaluation
88 constexpr Value LazyThreshold = Value(1500);
89 constexpr Value SpaceThreshold = Value(12222);
91 // KingAttackWeights[PieceType] contains king attack weights by piece type
92 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 77, 55, 44, 10 };
94 // Penalties for enemy's safe checks
95 constexpr int QueenSafeCheck = 780;
96 constexpr int RookSafeCheck = 880;
97 constexpr int BishopSafeCheck = 435;
98 constexpr int KnightSafeCheck = 790;
100 #define S(mg, eg) make_score(mg, eg)
102 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
103 // indexed by piece type and number of attacked squares in the mobility area.
104 constexpr Score MobilityBonus[][32] = {
105 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
106 S( 22, 26), S( 29, 29), S( 36, 29) },
107 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
108 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
109 S( 91, 88), S( 98, 97) },
110 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
111 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
112 S( 46,166), S( 48,169), S( 58,171) },
113 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
114 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
115 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
116 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
117 S(106,184), S(109,191), S(113,206), S(116,212) }
120 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
121 // pieces if they occupy or can reach an outpost square, bigger if that
122 // square is supported by a pawn.
123 constexpr Score Outpost[][2] = {
124 { S(22, 6), S(36,12) }, // Knight
125 { S( 9, 2), S(15, 5) } // Bishop
128 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
129 // no (friendly) pawn on the rook file.
130 constexpr Score RookOnFile[] = { S(20, 7), S(45, 20) };
132 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
133 // which piece type attacks which one. Attacks on lesser pieces which are
134 // pawn-defended are not considered.
135 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
136 S(0, 0), S(0, 31), S(39, 42), S(57, 44), S(68, 112), S(47, 120)
139 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
140 S(0, 0), S(0, 24), S(38, 71), S(38, 61), S(0, 38), S(36, 38)
143 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
144 constexpr Score PassedRank[RANK_NB] = {
145 S(0, 0), S(5, 18), S(12, 23), S(10, 31), S(57, 62), S(163, 167), S(271, 250)
148 // PassedFile[File] contains a bonus according to the file of a passed pawn
149 constexpr Score PassedFile[FILE_NB] = {
150 S( -1, 7), S( 0, 9), S(-9, -8), S(-30,-14),
151 S(-30,-14), S(-9, -8), S( 0, 9), S( -1, 7)
154 // PassedDanger[Rank] contains a term to weight the passed score
155 constexpr int PassedDanger[RANK_NB] = { 0, 0, 0, 3, 7, 11, 20 };
157 // Assorted bonuses and penalties
158 constexpr Score BishopPawns = S( 3, 7);
159 constexpr Score CloseEnemies = S( 6, 0);
160 constexpr Score Connectivity = S( 3, 1);
161 constexpr Score CorneredBishop = S( 50, 50);
162 constexpr Score Hanging = S( 52, 30);
163 constexpr Score HinderPassedPawn = S( 4, 0);
164 constexpr Score KingProtector = S( 6, 6);
165 constexpr Score KnightOnQueen = S( 21, 11);
166 constexpr Score LongDiagonalBishop = S( 22, 0);
167 constexpr Score MinorBehindPawn = S( 16, 0);
168 constexpr Score Overload = S( 10, 5);
169 constexpr Score PawnlessFlank = S( 20, 80);
170 constexpr Score RookOnPawn = S( 8, 24);
171 constexpr Score SliderOnQueen = S( 42, 21);
172 constexpr Score ThreatByKing = S( 23, 76);
173 constexpr Score ThreatByPawnPush = S( 45, 40);
174 constexpr Score ThreatByRank = S( 16, 3);
175 constexpr Score ThreatBySafePawn = S(173,102);
176 constexpr Score TrappedRook = S( 92, 0);
177 constexpr Score WeakQueen = S( 50, 10);
178 constexpr Score WeakUnopposedPawn = S( 5, 29);
182 // Evaluation class computes and stores attacks tables and other working data
187 Evaluation() = delete;
188 explicit Evaluation(const Position& p) : pos(p) {}
189 Evaluation& operator=(const Evaluation&) = delete;
193 template<Color Us> void initialize();
194 template<Color Us, PieceType Pt> Score pieces();
195 template<Color Us> Score king() const;
196 template<Color Us> Score threats() const;
197 template<Color Us> Score passed() const;
198 template<Color Us> Score space() const;
199 ScaleFactor scale_factor(Value eg) const;
200 Score initiative(Value eg) const;
205 Bitboard mobilityArea[COLOR_NB];
206 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
208 // attackedBy[color][piece type] is a bitboard representing all squares
209 // attacked by a given color and piece type. Special "piece types" which
210 // is also calculated is ALL_PIECES.
211 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
213 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
214 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
215 // pawn or squares attacked by 2 pawns are not explicitly added.
216 Bitboard attackedBy2[COLOR_NB];
218 // kingRing[color] are the squares adjacent to the king, plus (only for a
219 // king on its first rank) the squares two ranks in front. For instance,
220 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
221 // and h6. It is set to 0 when king safety evaluation is skipped.
222 Bitboard kingRing[COLOR_NB];
224 // kingAttackersCount[color] is the number of pieces of the given color
225 // which attack a square in the kingRing of the enemy king.
226 int kingAttackersCount[COLOR_NB];
228 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
229 // the given color which attack a square in the kingRing of the enemy king.
230 // The weights of the individual piece types are given by the elements in
231 // the KingAttackWeights array.
232 int kingAttackersWeight[COLOR_NB];
234 // kingAttacksCount[color] is the number of attacks by the given color to
235 // squares directly adjacent to the enemy king. Pieces which attack more
236 // than one square are counted multiple times. For instance, if there is
237 // a white knight on g5 and black's king is on g8, this white knight adds 2
238 // to kingAttacksCount[WHITE].
239 int kingAttacksCount[COLOR_NB];
243 // Evaluation::initialize() computes king and pawn attacks, and the king ring
244 // bitboard for a given color. This is done at the beginning of the evaluation.
245 template<Tracing T> template<Color Us>
246 void Evaluation<T>::initialize() {
248 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
249 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
250 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
251 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
253 // Find our pawns that are blocked or on the first two ranks
254 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
256 // Squares occupied by those pawns, by our king or queen, or controlled by enemy pawns
257 // are excluded from the mobility area.
258 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
260 // Initialise attackedBy bitboards for kings and pawns
261 attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
262 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
263 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
264 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
266 // Init our king safety tables only if we are going to use them
267 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
269 kingRing[Us] = attackedBy[Us][KING];
270 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
271 kingRing[Us] |= shift<Up>(kingRing[Us]);
273 if (file_of(pos.square<KING>(Us)) == FILE_H)
274 kingRing[Us] |= shift<WEST>(kingRing[Us]);
276 else if (file_of(pos.square<KING>(Us)) == FILE_A)
277 kingRing[Us] |= shift<EAST>(kingRing[Us]);
279 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
280 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
283 kingRing[Us] = kingAttackersCount[Them] = 0;
287 // Evaluation::pieces() scores pieces of a given color and type
288 template<Tracing T> template<Color Us, PieceType Pt>
289 Score Evaluation<T>::pieces() {
291 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
292 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
293 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
294 : Rank5BB | Rank4BB | Rank3BB);
295 const Square* pl = pos.squares<Pt>(Us);
299 Score score = SCORE_ZERO;
301 attackedBy[Us][Pt] = 0;
303 while ((s = *pl++) != SQ_NONE)
305 // Find attacked squares, including x-ray attacks for bishops and rooks
306 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
307 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
308 : pos.attacks_from<Pt>(s);
310 if (pos.blockers_for_king(Us) & s)
311 b &= LineBB[pos.square<KING>(Us)][s];
313 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
314 attackedBy[Us][Pt] |= b;
315 attackedBy[Us][ALL_PIECES] |= b;
317 if (b & kingRing[Them])
319 kingAttackersCount[Us]++;
320 kingAttackersWeight[Us] += KingAttackWeights[Pt];
321 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
324 int mob = popcount(b & mobilityArea[Us]);
326 mobility[Us] += MobilityBonus[Pt - 2][mob];
328 if (Pt == BISHOP || Pt == KNIGHT)
330 // Bonus if piece is on an outpost square or can reach one
331 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
333 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
335 else if (bb &= b & ~pos.pieces(Us))
336 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
338 // Knight and Bishop bonus for being right behind a pawn
339 if (shift<Down>(pos.pieces(PAWN)) & s)
340 score += MinorBehindPawn;
342 // Penalty if the piece is far from the king
343 score -= KingProtector * distance(s, pos.square<KING>(Us));
347 // Penalty according to number of pawns on the same color square as the
348 // bishop, bigger when the center files are blocked with pawns.
349 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
351 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s)
352 * (1 + popcount(blocked & CenterFiles));
354 // Bonus for bishop on a long diagonal which can "see" both center squares
355 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
356 score += LongDiagonalBishop;
359 // An important Chess960 pattern: A cornered bishop blocked by a friendly
360 // pawn diagonally in front of it is a very serious problem, especially
361 // when that pawn is also blocked.
364 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
366 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
367 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
368 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
369 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
376 // Bonus for aligning rook with enemy pawns on the same rank/file
377 if (relative_rank(Us, s) >= RANK_5)
378 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
380 // Bonus for rook on an open or semi-open file
381 if (pe->semiopen_file(Us, file_of(s)))
382 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
384 // Penalty when trapped by the king, even more if the king cannot castle
387 File kf = file_of(pos.square<KING>(Us));
388 if ((kf < FILE_E) == (file_of(s) < kf))
389 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
395 // Penalty if any relative pin or discovered attack against the queen
396 Bitboard queenPinners;
397 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
402 Trace::add(Pt, Us, score);
408 // Evaluation::king() assigns bonuses and penalties to a king of a given color
409 template<Tracing T> template<Color Us>
410 Score Evaluation<T>::king() const {
412 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
413 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
414 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
416 const Square ksq = pos.square<KING>(Us);
417 Bitboard weak, b, b1, b2, safe, unsafeChecks;
419 // King shelter and enemy pawns storm
420 Score score = pe->king_safety<Us>(pos, ksq);
422 // Main king safety evaluation
423 if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
428 // Attacked squares defended at most once by our queen or king
429 weak = attackedBy[Them][ALL_PIECES]
431 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
433 // Analyse the safe enemy's checks which are possible on next move
434 safe = ~pos.pieces(Them);
435 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
437 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
438 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
440 // Enemy queen safe checks
441 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
442 kingDanger += QueenSafeCheck;
444 b1 &= attackedBy[Them][ROOK];
445 b2 &= attackedBy[Them][BISHOP];
447 // Enemy rooks checks
449 kingDanger += RookSafeCheck;
453 // Enemy bishops checks
455 kingDanger += BishopSafeCheck;
459 // Enemy knights checks
460 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
462 kingDanger += KnightSafeCheck;
466 // Unsafe or occupied checking squares will also be considered, as long as
467 // the square is in the attacker's mobility area.
468 unsafeChecks &= mobilityArea[Them];
470 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
471 + 69 * kingAttacksCount[Them]
472 + 185 * popcount(kingRing[Us] & weak)
473 + 129 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
474 - 873 * !pos.count<QUEEN>(Them)
475 - 6 * mg_value(score) / 8
478 // Transform the kingDanger units into a Score, and subtract it from the evaluation
481 int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);
482 kingDanger = std::max(0, kingDanger + mobilityDanger);
483 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
487 Bitboard kf = KingFlank[file_of(ksq)];
489 // Penalty when our king is on a pawnless flank
490 if (!(pos.pieces(PAWN) & kf))
491 score -= PawnlessFlank;
493 // Find the squares that opponent attacks in our king flank, and the squares
494 // which are attacked twice in that flank but not defended by our pawns.
495 b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
496 b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
498 // King tropism, to anticipate slow motion attacks on our king
499 score -= CloseEnemies * (popcount(b1) + popcount(b2));
502 Trace::add(KING, Us, score);
508 // Evaluation::threats() assigns bonuses according to the types of the
509 // attacking and the attacked pieces.
510 template<Tracing T> template<Color Us>
511 Score Evaluation<T>::threats() const {
513 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
514 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
515 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
517 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safeThreats;
518 Score score = SCORE_ZERO;
521 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
523 // Squares strongly protected by the enemy, either because they defend the
524 // square with a pawn, or because they defend the square twice and we don't.
525 stronglyProtected = attackedBy[Them][PAWN]
526 | (attackedBy2[Them] & ~attackedBy2[Us]);
528 // Non-pawn enemies, strongly protected
529 defended = nonPawnEnemies & stronglyProtected;
531 // Enemies not strongly protected and under our attack
532 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
534 // Bonus according to the kind of attacking pieces
537 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
540 Square s = pop_lsb(&b);
541 score += ThreatByMinor[type_of(pos.piece_on(s))];
542 if (type_of(pos.piece_on(s)) != PAWN)
543 score += ThreatByRank * (int)relative_rank(Them, s);
546 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
549 Square s = pop_lsb(&b);
550 score += ThreatByRook[type_of(pos.piece_on(s))];
551 if (type_of(pos.piece_on(s)) != PAWN)
552 score += ThreatByRank * (int)relative_rank(Them, s);
555 // Bonus for king attacks on pawns or pieces which are not pawn-defended
556 if (weak & attackedBy[Us][KING])
557 score += ThreatByKing;
559 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
561 // Bonus for overload (non-pawn enemies attacked once or more and defended exactly once)
563 & attackedBy[Us][ALL_PIECES]
564 & attackedBy[Them][ALL_PIECES] & ~attackedBy2[Them];
565 score += Overload * popcount(b);
568 // Bonus for enemy unopposed weak pawns
569 if (pos.pieces(Us, ROOK, QUEEN))
570 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
572 // Our safe or protected pawns
573 b = pos.pieces(Us, PAWN)
574 & (~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES]);
576 safeThreats = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
577 score += ThreatBySafePawn * popcount(safeThreats);
579 // Find squares where our pawns can push on the next move
580 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
581 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
583 // Keep only the squares which are not completely unsafe
584 b &= ~attackedBy[Them][PAWN]
585 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
587 // Bonus for safe pawn threats on the next move
588 b = pawn_attacks_bb<Us>(b)
590 & ~attackedBy[Us][PAWN];
592 score += ThreatByPawnPush * popcount(b);
594 // Bonus for threats on the next moves against enemy queen
595 if (pos.count<QUEEN>(Them) == 1)
597 Square s = pos.square<QUEEN>(Them);
598 safeThreats = mobilityArea[Us] & ~stronglyProtected;
600 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
602 score += KnightOnQueen * popcount(b & safeThreats);
604 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
605 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
607 score += SliderOnQueen * popcount(b & safeThreats & attackedBy2[Us]);
610 // Connectivity: ensure that knights, bishops, rooks, and queens are protected
611 b = (pos.pieces(Us) ^ pos.pieces(Us, PAWN, KING)) & attackedBy[Us][ALL_PIECES];
612 score += Connectivity * popcount(b);
615 Trace::add(THREAT, Us, score);
620 // Evaluation::passed() evaluates the passed pawns and candidate passed
621 // pawns of the given color.
623 template<Tracing T> template<Color Us>
624 Score Evaluation<T>::passed() const {
626 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
627 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
629 auto king_proximity = [&](Color c, Square s) {
630 return std::min(distance(pos.square<KING>(c), s), 5);
633 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
634 Score score = SCORE_ZERO;
636 b = pe->passed_pawns(Us);
640 Square s = pop_lsb(&b);
642 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
644 bb = forward_file_bb(Us, s) & pos.pieces(Them);
645 score -= HinderPassedPawn * popcount(bb);
647 int r = relative_rank(Us, s);
648 int w = PassedDanger[r];
650 Score bonus = PassedRank[r];
654 Square blockSq = s + Up;
656 // Adjust bonus based on the king's proximity
657 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
658 - king_proximity(Us, blockSq) * 2) * w);
660 // If blockSq is not the queening square then consider also a second push
662 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
664 // If the pawn is free to advance, then increase the bonus
665 if (pos.empty(blockSq))
667 // If there is a rook or queen attacking/defending the pawn from behind,
668 // consider all the squaresToQueen. Otherwise consider only the squares
669 // in the pawn's path attacked or occupied by the enemy.
670 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
672 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
674 if (!(pos.pieces(Us) & bb))
675 defendedSquares &= attackedBy[Us][ALL_PIECES];
677 if (!(pos.pieces(Them) & bb))
678 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
680 // If there aren't any enemy attacks, assign a big bonus. Otherwise
681 // assign a smaller bonus if the block square isn't attacked.
682 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
684 // If the path to the queen is fully defended, assign a big bonus.
685 // Otherwise assign a smaller bonus if the block square is defended.
686 if (defendedSquares == squaresToQueen)
689 else if (defendedSquares & blockSq)
692 bonus += make_score(k * w, k * w);
694 else if (pos.pieces(Us) & blockSq)
695 bonus += make_score(w + r * 2, w + r * 2);
698 // Scale down bonus for candidate passers which need more than one
699 // pawn push to become passed, or have a pawn in front of them.
700 if ( !pos.pawn_passed(Us, s + Up)
701 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
704 score += bonus + PassedFile[file_of(s)];
708 Trace::add(PASSED, Us, score);
714 // Evaluation::space() computes the space evaluation for a given side. The
715 // space evaluation is a simple bonus based on the number of safe squares
716 // available for minor pieces on the central four files on ranks 2--4. Safe
717 // squares one, two or three squares behind a friendly pawn are counted
718 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
719 // improve play on game opening.
721 template<Tracing T> template<Color Us>
722 Score Evaluation<T>::space() const {
724 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
725 constexpr Bitboard SpaceMask =
726 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
727 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
729 if (pos.non_pawn_material() < SpaceThreshold)
732 // Find the available squares for our pieces inside the area defined by SpaceMask
733 Bitboard safe = SpaceMask
734 & ~pos.pieces(Us, PAWN)
735 & ~attackedBy[Them][PAWN];
737 // Find all squares which are at most three squares behind some friendly pawn
738 Bitboard behind = pos.pieces(Us, PAWN);
739 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
740 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
742 int bonus = popcount(safe) + popcount(behind & safe);
743 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
745 Score score = make_score(bonus * weight * weight / 16, 0);
748 Trace::add(SPACE, Us, score);
754 // Evaluation::initiative() computes the initiative correction value
755 // for the position. It is a second order bonus/malus based on the
756 // known attacking/defending status of the players.
759 Score Evaluation<T>::initiative(Value eg) const {
761 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
762 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
764 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
765 && (pos.pieces(PAWN) & KingSide);
767 // Compute the initiative bonus for the attacking side
768 int complexity = 8 * pe->pawn_asymmetry()
769 + 12 * pos.count<PAWN>()
771 + 16 * pawnsOnBothFlanks
772 + 48 * !pos.non_pawn_material()
775 // Now apply the bonus: note that we find the attacking side by extracting
776 // the sign of the endgame value, and that we carefully cap the bonus so
777 // that the endgame score will never change sign after the bonus.
778 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
781 Trace::add(INITIATIVE, make_score(0, v));
783 return make_score(0, v);
787 // Evaluation::scale_factor() computes the scale factor for the winning side
790 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
792 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
793 int sf = me->scale_factor(pos, strongSide);
795 // If scale is not already specific, scale down the endgame via general heuristics
796 if (sf == SCALE_FACTOR_NORMAL)
798 if ( pos.opposite_bishops()
799 && pos.non_pawn_material(WHITE) == BishopValueMg
800 && pos.non_pawn_material(BLACK) == BishopValueMg)
803 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
806 return ScaleFactor(sf);
810 // Evaluation::value() is the main function of the class. It computes the various
811 // parts of the evaluation and returns the value of the position from the point
812 // of view of the side to move.
815 Value Evaluation<T>::value() {
817 assert(!pos.checkers());
819 // Probe the material hash table
820 me = Material::probe(pos);
822 // If we have a specialized evaluation function for the current material
823 // configuration, call it and return.
824 if (me->specialized_eval_exists())
825 return me->evaluate(pos);
827 // Initialize score by reading the incrementally updated scores included in
828 // the position object (material + piece square tables) and the material
829 // imbalance. Score is computed internally from the white point of view.
830 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
832 // Probe the pawn hash table
833 pe = Pawns::probe(pos);
834 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
836 // Early exit if score is high
837 Value v = (mg_value(score) + eg_value(score)) / 2;
838 if (abs(v) > LazyThreshold)
839 return pos.side_to_move() == WHITE ? v : -v;
841 // Main evaluation begins here
846 // Pieces should be evaluated first (populate attack tables)
847 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
848 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
849 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
850 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
852 score += mobility[WHITE] - mobility[BLACK];
854 score += king< WHITE>() - king< BLACK>()
855 + threats<WHITE>() - threats<BLACK>()
856 + passed< WHITE>() - passed< BLACK>()
857 + space< WHITE>() - space< BLACK>();
859 score += initiative(eg_value(score));
861 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
862 ScaleFactor sf = scale_factor(eg_value(score));
863 v = mg_value(score) * int(me->game_phase())
864 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
866 v /= int(PHASE_MIDGAME);
868 // In case of tracing add all remaining individual evaluation terms
871 Trace::add(MATERIAL, pos.psq_score());
872 Trace::add(IMBALANCE, me->imbalance());
873 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
874 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
875 Trace::add(TOTAL, score);
878 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
885 /// evaluate() is the evaluator for the outer world. It returns a static
886 /// evaluation of the position from the point of view of the side to move.
888 Value Eval::evaluate(const Position& pos) {
889 return Evaluation<NO_TRACE>(pos).value();
893 /// trace() is like evaluate(), but instead of returning a value, it returns
894 /// a string (suitable for outputting to stdout) that contains the detailed
895 /// descriptions and values of each evaluation term. Useful for debugging.
897 std::string Eval::trace(const Position& pos) {
899 std::memset(scores, 0, sizeof(scores));
901 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
903 Value v = Evaluation<TRACE>(pos).value();
905 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
907 std::stringstream ss;
908 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
909 << " Term | White | Black | Total \n"
910 << " | MG EG | MG EG | MG EG \n"
911 << " ------------+-------------+-------------+------------\n"
912 << " Material | " << Term(MATERIAL)
913 << " Imbalance | " << Term(IMBALANCE)
914 << " Initiative | " << Term(INITIATIVE)
915 << " Pawns | " << Term(PAWN)
916 << " Knights | " << Term(KNIGHT)
917 << " Bishops | " << Term(BISHOP)
918 << " Rooks | " << Term(ROOK)
919 << " Queens | " << Term(QUEEN)
920 << " Mobility | " << Term(MOBILITY)
921 << " King safety | " << Term(KING)
922 << " Threats | " << Term(THREAT)
923 << " Passed | " << Term(PASSED)
924 << " Space | " << Term(SPACE)
925 << " ------------+-------------+-------------+------------\n"
926 << " Total | " << Term(TOTAL);
928 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";